Phantasmal, when I reply to a post that is right above mine, it's pretty obvious I am responding to it.
The devs decide the criteria on what banners are acceptable. Apparently it's the devs that feel that certain banners ruin the immersion and the atmosphere of the game they want to create. I happen to agree. If it's such a barrier to your enjoyment of the game, and a sizeable number of other people feel likewise, maybe you can get them to change their opinion.
The idea that all banners have to be historically correct heraldry for the era is bullshit. As Penguin points out, the Merc banner is not a stylized representation but a realistic comp generated design. It would be out of place if that was the criteria. Personally I don't see much wrong with Ary's peasant banner appart from the offensive purple vomit, but that's mostly a subjective esthetic call. It fits the theme of his clan, which itself fits well into Warband and cRPG. Peasants with pitchforks are a stapple of the game. There's a world of difference between that and some of the other banners that got banned.